This invention relates generally to a ferrite rod antenna. More particularly, the present invention relates to a ferrite rod antenna wherein a single piece of wire forms both the antenna coil and a retention means for the antenna assembly.
Antenna elements have been down sized in order to meet the manufacturing and size constraints which accompany the trend towards smaller paging and radio receiver packages. Such antennas, however, must nevertheless provide a sufficiently high (Q) while simultaneously exhibiting sufficient radiated signal sensitivity.
U.S. Pat. No. 3,267,478, issued Aug. 16, 1966 describes an antenna which comprises a cylindrical core surrounded by a sleeve of electrically conductive material. A gap runs the entire length of the sleeve and has a plurality of capacitors distributed throughout its length. A coupling winding surrounds at least a portion of the core and includes a pair of wires for coupling the antenna assembly to the receiver. Unfortunately, the antenna provides no means for readily mounting the antenna assembly to a printed circuit board. Thus, this antenna system would not be suitable for use in conjunction with todays more complex mounting and circuit interconnection techniques.
Similarly, U.S. Pat. No. 3,594,805, issued Jul. 20, 1971 describes an antenna in which the resonant frequency may be adjusted by varying the inductance of a first split sleeve. The opposite edges of the longitudinal split are connected by a plurality of capacitors uniformly distributed over the length of the sleeve. The first sleeve additionally includes a longitudinal slot approximately one third the length of the rod. A second split sleeve is positioned over the first sleeve to adjust the inductance of the assembly by masking poritons of the longitudinal slot. As was the case before, no adequate means are disclosed for mounting the antenna assembly to a printed circuit board. Furthermore, wire leads are necessary for forming the electrical connections between the circuit and the antenna.
U.S. Pat. No. 3,946,397, issued Mar. 23, 1976 discloses an antenna arrangement which includes a spiral inductor or coil which is divided into a number of segments interconnected by individual capacitor elements to form a number of series resonant circuits. While an effective antenna technique, this arrangement still does not describe a simple mechanism for implementation and connection to a printed circuit board.
In an effort to overcome the above described disadvantages, U.S. Pat. No. 4,814,782, issued Mar. 21, 1989 discloses an antenna which includes a generally elongate, magnetically permeable core having a major axis and an insulating substrate affixed along an axis parallel to the major axis. The insulating substrate has a plurality of opposed pairs of conductive runners positioned at generally regular intervals along the substrate normal to the major axis. A plurality of discrete capacitors are secured between opposite pairs of conductive runners. An electrically conductive split sleeve substantially surrounds the core and has pairs of opposed tabs on the edge portions in electrical connection with the opposed pairs of conductive runners. The sleeve further includes integral mounting tabs for securing the antenna assembly to the printed circuit board to establish electrical connection to the antenna without the use of wire leads.
Unfortunately, the system described in this latter patent involves an assembly process which is both complex and costly. For example, the capacitors are attached to the printed circuit board by a reflow process, and the sleeve is hand soldered. The ferrite core or rod must be aligned in the sleeve and then glued thereto. The ferrite core is also glued to the printed circuit board.
In a low band version of this antenna assembly, a copper strip is wrapped around the ferrite core (i.e. 5 turns). The strip is aligned, and the assembly is then subjected to a shrink wrap process. The shrink wrap is then cut to expose the leads, the assembly is glued to the printed circuit board, and the leads are soldered.
These processes are complex, time consuming, and result in an arrangement which is easily damaged during normal use. It would therefore be highly desirable to provide a ferrite rod antenna assembly which can be easily mounted and electrically connected to a printed circuit board.